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6.7 What does "Unknown filetype" mean?

Q: I get error messages saying "Unknown filetype" from GCC.

Q: Since a few days ago, whenever I try to run most of the DJGPP programs, they print a message "C:\DJGPP\BIN\prog.exe: not COFF" and just terminate. Help!!!

A: It might be that your DJGPP programs and/or STUBIFY.EXE are infected by a virus. (This is not a joke! It did happen to a few of us and can happen even to you.) As the DOS stub prepended to the DJGPP programs is very short, many viruses cannot attach themselves to it without overwriting the beginning of the DJGPP COFF image which specifies vital information such as location and length of various program sections, therefore triggering this error from the code in the stub that loads the COFF image.

Another possible cause of the "Unknown filetype" message is that you mix a v2.0 gcc.exe driver with cc1plus.exe, cc1.exe or other programs from an old v1.x distribution.